Ink utilization in writing instruments



g- 1967 G. R URQUHART INK UTILIZATION IN WRITING INSTRUMENTS Filed Oct.

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United States Patent This invention pertains to improved and more complete utilization of ink in writing instruments and is particularly directed to means and methods whereby substantially the entire volume of ink initially charged into a cartridge or reservoir of a ball point type writing instrument is capable of being utilized in writing with such instrument.

Normal ball point writing instruments generally include a tubular cartridge or reservoir, the forward end thereof being in communication with or at least attached to a writing tip, including a socket in which a ball is rotatably held. The cartridge is filled with a suitable ink and the rear end of the cartridge is generally placed in communication with the atmosphere, although in some instances a gas under pressure may be superimposed upon the surface of the ink in the cartridge. When the rear end of the cartridge is exposed to the atmosphere or to a gas, the ink at the surface of the body of ink may either oxidize, dry or be otherwise deleteriously affected by the air or gas. Moreover, since ball point writing instruments of this type are sometimes carried in the pocket with the writing tip pointed upwardly or permitted to rest in a horizontal position for protracted periods of time, there is tendency for the ink to ooze out of the open end (referred to as back leakage"). Also, when the rear end of the cartridge is enclosed and supplied with a source of gas under pressure, the ink may move rearwardly towards the closed end and entrap bubbles of gas within the body of ink so that subsequent utilization of the pen is not very satisfactory since bubbles of air in the very small diameter channels leading to the ball socket will interrupt the flow of ink to the socket and cause the pen to discontinue writing. Back leakage is undesirable since it may stain clothing, reduce writing ability, etc. The aforesaid difficulties have been overcome in the past to some extent by placing a follower, such as a body of grease, on the rear surface of the ink within the cartridge, the viscous follower protecting the surface from the action of the air or gas and following the ink by maintaining contact with the surface as the body of ink travels toward the tip due to reduction of ink supply during writing. It is to be remembered that ball point pens write by withdrawing ink from a channel leading to the socket and depositing the ink on the writing surface.

However, when the volume of ink in a reservoir or cartridge has been reduced to a minor percentage of the initial charge, particularly in cartridges having a main reservoir exceeding in cross-sectional area equivalent of a 0.1" diameter, and such larger tubes are then connect ed to the writing tip by a smaller tube of say 0.1 or 0x9" I.D., the Writing function of the pen is interrupted when the follower reaches the constriction or attempts to enter the small diameter tube or the even smaller channels leading to the writing socket itself. As a result, an appreciable quantity of ink remains unused in the cartridge and cannot be written out. Moreover, the interruption in writ ing function is not a clear-cut termination but is often ac companied by a decrease in the amount of ink made available to the writing ball causing the writing trace to become indistinct or interrupted in part, thereby causing the writer to feel that the instrument is malfunctioning and has not been depleted of its ink.

The presentinvention is directed to this problem and to means and methods of eliminating the problem. Generally stated, the invention distinguishes from prior practices in that instead of employing a unitary follower, such a body of grease, there is now employed a viscous or viscoplastic follower in contact with the walls of the reservoir and with a centrally disposed elongated virtually rigid element which interrupts the previously continuous contact between grease and top ink surface. Moreover, the central element preferably also extends through and iuterrupts the continuity of the top surface of the body of viscous follower, although the existence of a thin film over the element is permissible. The assembly of viscous follower and element is herein referred to as a follower assembly since it moves downwardly with the surface of the ink body as the latter is depleted during writing. The element may be cylindrical, or it may be axially bored; when so bored, the axial port may contain additional viscous follower or a loosely fitting pin with grease between the pin and bore wall in the element. By employing ink, element (or elements) and viscous follower of successively lower specific gravity, the operation of the assembly in attaining the objects of this invention is facilitated.

An object of the present invention, therefore, is to disclose means and methods whereby substantially the entire volume of ink initially charged into a cartridge or reser' voir of a writing instrument is capable of being utilized in writing with such instrument, and no appreciable quantity of ink is wasted or remains incapable: of use.

Another object is to disclose means and methods for effectively utilizing the entire volume of ink, initially charged into a cartridge or reservoir of a ball point type pen, in performing normal writing functions without objectionable interruptions of such writing function when the ink charge has been reduced to a minor percentage of the initial charge.

A still further object is to insure a termination of the writing function only when the body of ink initially charged into the writing instrument has been depleted, thereby eliminating the false interruptions of writing function caused by premature impairment of ink movement to the ball point tip, which false movement generally occurs in prior writing instruments of this type and constitutes a source of annoyance.

Although the present invention is applicable to various pens, both of the retractable type as well as of the nonretractable type, and to cartridges which are of substan' tially uniform internal diameter, as well as cartridges ineluding a main reservoir of a diameter exceeding 0.1", the following drawings appended hereto and used for purposes of illustration and explanation will refer to the utilization of the invention in cartridges which are replaceable and which do include an enlarged main ink reservoir.

In the drawings:

FIG. 1 is a representation of a writing instrument including one form of cartridge (portions of the body being broken away) whereby the relationship of the cartridge to the pen body and retraction mechanism can be readily understood.

FIG. 2 is an enlarged side view of a portion of a cartridge, the wall of the cartridge being partly broken away, illustrating one form of composite follower assembly embodying the present invention.

FIG. 3 illustrates the position of the follower assembly of FIG. 2 shortly after it had reached the constriction in the cartridge.

FIG. 4 is an enlarged axial section of a portion of a cartridge illustrating another modified form of follower assembly utilizing the present invention, the follower as sembly having reached a constriction in the reservoir.

FIG. 5 in a transverse section of a cartridge containing a follower as in FIG. 4, showing a plan View of the follower assembly.

FIG. 6 is an axial section through a portion of a cartridge including a still further modification of a follower assembly.

FIG. 1 somewhat diagrammatically represents a complete writing instrument of the ball point type including an outer barrel composed of a forward barrel section 1 and a removable cap portion 2 which normally includes a retraction mechanism generally indicated at 3 and often actuated by a rearwardly extending plunger 4. Since various retraction mechanisms are known in the art, details are not shown. Removable positioned within the pen body or barrel is a cartridge or ink reservoir 10 provided with a writing tip 11 which is capable of being projected from or retracted into the lower end of the barrel by the retracting mechanism 3. In most instances retraction is facilitated by the action of a spring bearing against an abutment formed on the interior surface of the barrel and against an enlargement or shoulder formed in the cartridge 10.

The cartridge illustrated in FIG. 1 includes an upper reservoir section 12 of relatively large diameter and an auxiliary tubular reservoir 13 of smaller internal diameter into which the tip 11 extends. The tip 11 (as more clearly shown in FIG. 3) includes very small ink channels 14 leading to a socket containing a rotatable ball 15. The rear end of the cartridge may be provided with a plug having a rearwardly extending projection 16 which is axially bored to permit air to enter the rear part of the cartridge. A body of ink is contained within the cartridge, such body of ink being continuous in that it fills the enlarged or main reservoir section 12, the smaller reservoir 13 and the channel 14, thereby insuring a continuous, unbroken supply of ink to the writing ball 15. Superimposed upon the upper surface of the body of ink within the cartridge, there is generally placed a viscous follower or small body of grease generally indicated at 18.

During writing, the body of ink within the reservoir is depleted and the grease follower 18, being in contact with the top surface of the ink as well as with the walls of the cartridge, follows the ink as its level drops. The body of grease 18 maintains its coherence and integrity and is preferably insoluble in and immiscible with the ink; it is also preferably of a non-drying character, To prevent back leakage, it has been found desirable to use viscous follower materials having a gel strength or yield strength on the order of 800 to 1100 dyne per square centimeter in order to prevent the material from shearing or being excessively deformed when a writing instrument of this type is in an inverted or horizontal position for a protracted period of time (as during storage). However,

when the body of ink has been partially depleted so that the ink level now drops to the tapered section 17 (interconnecting the large diameter reservoir 12 and auxiliary reservoir 13), it has been found that the grease does not shear and deform, under the forces existing, so as to successfully follow the ink down through the reservoir 13 of smaller diameter. Instead, the body of grease 18 will assume a position such as is indicated in dash lines at 181) and act as a plug. As a result, writing ability of the instrument becomes unsatisfactory; the supply of ink to the writing ball is interrupted; the user is annoyed since the interruption may be momentary or the trace left by the ball becomes weak for a short period of time and then a minute additional quantity of ink manages to get through the passageways so as to permit writing for another minute or two, and then becomes interrupted again. Eventually, the writing ability decreases to zero and the remaining portion of ink contained in the auxiliary reservoir section 13 and channels of the tip is rendered useless and wasted.

FIG. 2 is an enlarged side elevation partly in section of the same general type of cartridge as that illustrated in FIG. 1, but equipped with a follower assembly which provides a solution to the problem referred to hereinabove. In the form illustrated in FIG. 2, the follower assembly includes a relatively rigid or solid smooth-surfaced tubular element 20 positioned within a body of grease 28 and interrupting the continuity of such body inasmuch as the grease surrounds the tubular element 21 thereby spacing it from the internal walls of reservoir section 12 and also fills the central or axial bore 21 within the tubular element 20. Under preferred conditions, the grease 28 does not extend completely across from wall to Wall within the cartridge since the upper end of element 20 is not covered by the grease but extends thereabove. Similarly, the lower and conical end 22 of the element 20 preferably extends below the body of grease into the ink indicated at 30. In the illustrated embodiment, the outer diameter of element 20 is larger than the internal diameter of section 13 of the cartridge, but materially smaller than the internal diameter of main reservoir 12.

The element 20 may be made of any thermoplastic or thermosetting resinous composition which may include any desired polymer or copolymer capable of producing a relatively solid or rigid, preferably smooth-surfaced element having a specific gravity lower than that of the ink and greater than that of the grease. For purposes of illustration, it may be noted that inks commonly employed in ball point pens may have a specific gravity of from about 1.100 to 1.185 and the viscous follower material may have a specific gravity of from about 0.90 to about 0.95. As a result, a polyethylene, polyvinyl, polyamide or polystyrene follower element 20 having a specific gravity of from about 0.97 to about 1.09 may be employed.

FIG. 3 illustrates the position of such a follower shortly after it has reached the conical or tapering section 17 of the cartridge and the ink level has dropped until its surface is at or below the top of the tubular auxiliary reservoir section 13, or where said section merges into the conical restriction 17. As shown in the drawings, the lower annular edge of the element 20 is tapered so as to contact the conical wall 17 and position its smooth axial bore 21 in substantial alignment with the axis of the smaller tubular reservoir 13. As the ink level drops in the tubular section 13, the body of grease contained within the bore 21 of the element 20 will emerge from such bore and fol low the body of ink 30 as indicated at 28 in FIG. 3. It will be noticed that this section of grease 28, although it may have a high shear strength, is not subject to shear or deformation and readily slides along the surfaces of the bore 21 in the element 20 so as to readily follow the body of ink down through the small diameter reservoir 13. A boundary layer flow appears to take place when the core of grease leaves the solid element to follow the body of ink into the reservoir portion 13, writing terminating sharply when the grease reaches the tip, particularly when bore 21 is smaller than the internal diameter of 13.

By reason of the construction, arrangement and means described, a totally different result is obtained and all of the ink contained within the small auxiliary reservoir 13 may be eifectviely utilized for writing. This novel and utilitarian result is attained by the new follower assembly and its different mode of operation.

FIGS. 4 and 5 refer to a modified form of follower assembly wherein the annular or hollow cylindrically formed plastic element 20 now loosely and slidably contains another plastic element 23 in the form of a smoothsurfaced solid cylinder or pin. The grease 28 surrounds the element 20 and is also contained between the pin 23 and the inner bore 21 of element 20. In FIG. 4, the follower assembly is shown when it reaches the constriction, contacts the conical walls of the section 17 of the cartridge and the ink level now starts to descend through the auxiliary reservoir 13. The diameter of the inner bore 21 of element 20 is very slightly larger than and not appreciably smaller than the inner diameter of the section 13 of the cartridge; the outer diameter of the pin 23 is smaller than the inner diameter of section 13; a radial clearance of between about 0.01 to 0.03 between the inner bore 21 and outer surface of pin 23 provides adequate space for grease therebetween and proper functioning. As the ink level now drops, the grease-encased pin 23 slides out of the bore 21 of element 20 (which has been stopped by the conical constriction 17 of the cartridge) and follows the body of ink until such pin 23 reaches the dash-lined position, 23

thereby not only permitting the ink contained in auxiliary reservoir to be completely used in continuous writing, but finally positively and sharply terminating the writing operation by contacting (and in efiect sealing off) the passageway or channel 14 which extends through the writing tip 11 to the minute writing ball 15.

FIG. 6 illustrates a modification wherein the rigid element of the follower assembly is an elongated element having an upper, virtually cylindrical portion 24 whose greatest diameter is slightly smaller than the inner diameter of reservoir section 13, and an axially aligned lower extension 25 of even smaller diameter, the lowermost portion 26 of such extension being adapted to at least partially enter the writing tip 11 and channel 14 therein. Suitable inclined or conical surface areas may interconnect the upper portion 24 with the lower portions of smaller diameter whereby the element is provided with a smooth, unrecessed surface. This form of follower element desirably has a head portion 24 having a volumetric displacement at least equal to (and preferably somewhat greater than) that of its lower extension; the length of section 24 is preferably from 20% to 40% (or even 50%) of the length of the entire element. After a cartridge is filled with ink, a body of grease is placed upon the surface of the ink and the element is inserted thereinto so as to extend therethrough, the head portion 24 being surrounded by and spaced from the inner walls of the cartridge by a body of grease whereas the extension 25 extends into the ink therebelow. Such follower assembly will move downwardly with the ink (as the supply of ink is depleted during use) and the solid element will eventually pass into the small diameter reservoir section 13, a large portion of the grease being left upon the inclined walls 17 of the cartridge. When the length of head portion 24 is about 1.5 times its diameter, the device readily assumes an axial position. Finally, the extension 26 will locate itself in the tip 11 and channel 14 thereof, plug such channel and cause an abrupt, positive termination of writing, concurrent with the virtual exhaustion of the ink supply.

The modification illustrated in FIG. 6 exemplifies the solid plug element of a follower assembly; a plug element of similar external contours but having a small axial bore (say about 0.02 inch in diameter) can also be used, and any grease contained in the upper portion of such bore immediately after the follower assembly is installed above a body of ink in a reservoir cartridge will, after the element reaches its lower limit of travel in the cartridge, move downwardly through said bore to follow the ink to the writing tip and cause an abrupt termination of writing when the supply of ink is exhausted.

The follower assembly of this invention (in its various forms) is placed in position and in cooperative contact with the contact with the upper surface of ink in a cartridge or reservoir, preferably after ink has been charged into a reservoir and preferably after such ink-filled reservoir has been subjected to preliminary centrifuging whereby all channels and ink passageways to the ball socket have been filled with ink and air bubbles (if any) have been eliminated. In many cases, preliminary centrifuging is not necessary. A measured amount of viscous follower material and the solid follower element or elements are then inserted into the rear of the cartridge and the cartridge subjected to centrifugal forces to insure proper contact between the follower assembly and the surface of the ink. The quantity of viscous material employed is preferably insuflicient to form a materially thick layer extending over the upper end of the solid follower component after such final centrifuging.

Various greases may be used, generally composed of an oleaginous component (non-drying viscous oil or silicone) with or without a soap or thickening agent such as a colloidal material or salt of a fatty acid (such as aluminum stearate, zinc stearate, etc.). Other additives such as oxidation inhibitors, colloidals fillers, gel formers, etc.

6 may be present. The plastic, viscous, or visco-elastic follower employed should preferably not exhibit a marked ability of spreading upon the inner surfaces of the reservoir: such tendency may be reduced bysuitablechange in composition or pre-treatment of surfaces of the cartridge.

Although as previously indicated, the grease heretofore employed has had a gel strength of yield strength of between about 800 to about 1100 or even 1250 dyne per square centimeter, the grease employed in the follower assemblies of this invention may have a lower yield strength (as low as 250 dyne per square centimeter) even when the assembly is used in writing instruments having a main reservoir of 0.2 inch internal diameter. Ordinarily however, the internal diameter of large capacity reservoirs of ball point pens is on the order of 0.170 inch and of normal reservoirs on the order of 0.100 inch. It is to be understood that, if desired, the follower assemblies of this invention may be used in normal. reservoirs. Moreover, the gel strength of viscous follower materials adapted for use in the method and follower assembly of this invention may also be very much higher, i.e., a gel strength on the order of 22002500 dyne per square cm. can be used in a follower assembly of this invention, whereas such high gel strength follower material would be unusable alone.

The gel strength of a grease may be determined in several Ways, one of which involves the breaking strength of a column of grease. For example, a syringe is loaded with a grease to be tested, the syringe being fitted with a 13 gauge needle and the needle filled with grease from the syringe. It is desirable to allow the grease to age for a period of time to permit it to recover from the work softening that sometimes occurs during filling of the needle. The syringe is then mounted vertically, needle down, over a weighed receiver. Grease is extruded l0 mgs. at a time at one minute intervals until the pendant grease column breaks or shows that it would break. The column is in the latter case allowed to break under its own weight, even when several minutes are required for the breaking process to go to completion. The grease caught in the receiver is weighed to determine the tension on the grease column when it broke. From this tension and the inside diameter of the needle, the breaking strength in dynes per square centimeter is calculated.

Relative gel strength can also be determined by extruding the grease from a tube of larger diameter than a needle, say from a brass tube having an inside diameter of extrusion continuing slowly until the weight of the extruded grease exceeds its gel strength and a drop of grease breaks off.

In the light of the disclosures made herein, those familiar with the art will recognize that various changes and modifications can be made, while employing the modes of operation and assemblies of this invention, to attain the novel and useful results. All changes coming within the scope of the appended claims are embraced thereby.

I claim:

1. A follower assembly for use in a tubular writing cartridge having a writing socket tip at one end thereof, an ink reservoir portion of small diameter in communi cation with said tip and an ink reservoir of large diameter in communication with said reservoir portion, and a body of ink in said reservoir and small reservoir portion, whereby virtually the entire body of ink may be utilized in writing, comprising:

a solid element centrally and movably positioned in said reservoir, said element having an outer diameter larger than said reservoir portion, said element having a through axial bore in alignment with the reservoir portion, the lower end of said element being in contact with the top surface portion of a body of ink in said reservoir;

bodies of viscous follower material within the axial 7 bore of said tubular element and between said element and walls of said reservoir, said bodies of viscous material being in contact with the top Surface of said body of ink;

said tubular element being incapable of movement into the reservoir portion of small diameter while the body of viscous material within said tubular element is adapted to follow the ink into the reservoir portion.

2. A follower assembly as stated in claim 1 including a cylindrical solid element positioned within the body of viscous follower material within said tubular element, said cylindrical solid element being adapted to follow the ink into the reservoir portion and into proximity to the writing socket tip.

3. A follower assembly as stated in claim 1 wherein the viscous follower material has a gel strength of between 250 and about 2200 dyne per square centimeter.

4. A follower assembly as stated in claim 1 wherein the tubular element is provided with a lower conical surface adapted to contact the cartridge at a zone where the small diameter reservoir portion communicates with the ink reservoir.

5. A follower assembly as stated in claim 1 wherein the tubular element has a specific gravity lower than that of a body of ink in said reservoir and greater than that of the viscous follower material.

6. A follower assembly as stated in claim 1 wherein the tubular element is provided with a downwardly directed extension of smaller diameter than said reservoir portion and the axial bore extends through the element and its extension.

References Cited UNITED STATES PATENTS 3,082,740 3/1963 Eckerle 12042.4

FOREIGN PATENTS 646,258 8/1962 Canada. 971,301 7/1950 France. 798,897 7/1958 Great Britain.

LAWRENCE CHARLES, Primary Examiner. 

1. A FOLLOWER ASSEMBLY FOR USE IN A TUBULAR WRITING CARTRIDGE HAVING A WRITING SOCKET TIP AT ONE END THEREOF, AN INK RESERVOIR PORTION OF SMALL DIAMETER IN COMMUNICATION WITH SAID TIP AND AN INK RESERVOIR OF LARGE DIAMETER IN COMMUNICATION WITH SAID RESERVOIR PORTION, AND A BODY OF INK IN SAID RESERVOIR AND SMALL RESERVOIR PORTION, WHEREBY VIRTUALLY THE ENTIRE BODY OF INK MAY BE UTILIZED IN WRITING COMPRISING: A SOLID ELEMENT CENTRALLY AND MOVABLY POSITIONED IN SAID RESERVOIR, SAID ELEMENT HAVING AN OUTER DIAMETER LARGER THAN SAID RESERVOIR PORTION, SAID ELEMENT HAVING A THROUGH AXIAL BORE IN ALIGNMENT WITH THE RESERVOIR PORTION, THE LOWER END OF SAID ELEMENT BEING IN CONTACT WITH THE TOP SURFACE PORTION OF A BODY OF INK IN SAID RESERVOIR; 